OSU researchers create "shoulder arthrometer"

05/30/2000

CORVALLIS - A collaborative research team from Oregon State University has created a new instrument that can measure the degree of laxity or stiffness of the shoulder - a development that could help physicians better diagnose and treat athletes with sho ulder dislocations and other injuries.

The "shoulder arthrometer" already has shown that there may be a difference in the physiology of the shoulder between males and females.

And the instrument's ability to provide more precise measurements of shoulder movements may help determine if athletes in certain sports - including volleyball spikers, baseball pitchers and wheelchair competitors - are more at-risk for shoulder injuries.

The university has a provisional patent on the new device. The team presented its research at the recent annual meeting of the American Academy of Orthopaedic Surgeons, where it was featured on the front page of the physicians' research bulletin.

A working shoulder arthrometer would be big news in orthopedic circles, the researchers say. "If a person dislocates their shoulder, that shoulder will likely become 'looser' than it was prior to their injury," said Eric L. Sauers, a doctoral student in sports medicine at OSU and a member of the research team. "Following multiple dislocations th e usual procedure is to fold the stretched joint capsule back over itself and sew it, or use thermal energy to shrink the tissues to 'tighten' the shoulder capsule.

"But there hasn't been an objective value system that measures the laxity or tightness of the shoulder to adequately evaluate the severity of the injury, or to see how close the 'surgical repair' comes to approximating the previous condition," he added. "So it becomes rather subjective."

According to the OSU researchers, the relative tightness or laxity of a person's shoulder is typically measured only from a scale of "1" (when the shoulder is so tight the ball of the socket doesn't reach the rim) to a "3" (when it is so loose it moves o ver the rim). A measurement of "2" is somewhere in between.

With their new arthrometer, the researchers can measure movement of the shoulder's ball-and-socket joint to one-tenth of a millimeter.

Equally important, they say, is the instrument's ability to measure the stiffness or spring-like response of the shoulder.

"If I'm from the World Wrestling Federation, I can probably apply a lot more force to the shoulder than the average person," said Derald Herling, an assistant professor in the OSU Department of Mechanical Engineering. "Measuring movement isn't enough. If you are going to measure small movements, you have to be able to measure and control the force applied as well."

The shoulder, Herling says, presents a much more complex engineering challenge than, say, the knee. The knee moves primarily in one direction, he pointed out, while the shoulder has several degrees of movement.

"In aviation terms, you'd equate it to measuring the plane's elevation, latitude and longitude - or three positions - as well as the yaw, pitch and roll, or three rotations, at the specified position," Herling said.

The OSU-designed instrument already is showing its usefulness.

A prototype was used in a research project by Sauers and Herling that compared the shoulder movement of men and women who are active in recreational fitness, but who are not competitive "overhead" athletes (athletes using primarily an overhead arm movemen t). That study found that women had significantly greater shoulder laxity than men, though it is too soon to tell if that puts them at-risk for certain sports.

Sauers said the instrument eventually will be used to gather baseline data to find a normal range of motion for males and females. Once a value system is created, researchers could then evaluate the risk factors related to those measurements, and gauge t he effects on shoulder health of certain sports and of specialized activities within those sports. They could compare shoulder motions of men and women, or of youths and seniors.

They also could compare the tightness or laxity from persons' "healthy" shoulders to their injured shoulders. And they could, for the first time, accurately measure the tightness or laxity of a person's shoulder before and after an injury.

"The biggest advantage of the instrument is that it could give the physician another tool to aid in the diagnosis and treatment of shoulder injuries," Sauers said.

In addition to Sauers and Herling, former OSU faculty member Paul Borsa played a key role in the development of the instrument and continues to collaborate on the project. He now is on the faculty of the University of Michigan.